It took more than two hours for crews to snuff out an apartment fire in Denver early Wednesday morning.

The Denver Fire Department received its first call about the blaze at 3700 North Marion Street just before 1:30 a.m.

When crews arrived on scene, heavy smoke and flames were coming from the windows of the building, Denver Fire Department spokesman Mark Watson said.

Watson said initially firefighters fought the blaze inside the 2- and 3-story building, which is home to about six to eight units. However, as the building became compromised, crews withdrew and battled the fire from the exterior.

Everyone inside the building was able to evacuate and no injuries were reported, Watson said.

“At this point in time, there is no indication as to the origin or cause of the fire,” Watson said.

Three sides of the building collapsed during the fire, Watson said, which is hampering the investigation.

The building sits on a corner and has power lines running around it, which further complicated matters for firefighters. Watson said it was difficult for crews to get into their aerial firefighting apparatus.

Building engineers were called to the scene Wednesday morning to assess the damage to determine when investigators might be able to get inside.

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